A couple of ideas..........

First off, if you're interested in keeping the scale outline as pristine as possible, you need to consider the Slimline "sport" Pitts mufflers. Their pipes come out 90degrees different than the regular Pitts mufflers. The difference might allow you to mount the engine completely cowled and still have the pipes also go down. And if that works but the pipes don't reach out far enough, get those flexible exhaust extensions and use them (or just use the straight part of them).

And about how an inverted engine runs..... What you encounter is that they're SOMETIMES harder to start. They're going to run fine. And how they start is biased by two things. One is that the usual carb placement (upside down) means the engine is actually going to be harder to flood through the carb when filling the tank. And the other is that it might have a tendency to flood once you start flipping the prop, or finger choking, or trying to prime it. All of those things are well within our ability to control.

So the bottom line on starting an inverted engine is that we have to simply pay attention to each one and see what set of details each engine needs.

I flew competition CL precision aerobatics for years and years. You have to signal when you're ready to begin your official flight attempts AND THEN start your engine. And you're on the clock while starting that engine. And your flight time is finite. The judges quit scoring you when your total time runs out PLUS you also lose the "full flight" bonus! And nobody had electric starters. We all hand cranked the suckers. And darn near every model had a tightly cowled, upside down engine. And I don't remember in all those years but only a couple of guys who couldn't get a one or two flip start. Those guys simply paid attention to how they filled the tank. And how they primed the sucker. And what condition the glow plug was in. And the guys who couldn't get their engines to start almost always had trouble no matter what engine they had at the time. They either didn't or couldn't pay attention to the fueling and priming details.

I use a hand crank fuel pump. I count the number of revolutions it takes for each model to fill the tank. I watch the "overflow" fuel line like a hawk when fueling. When fuel shows, I stop cranking and do 1/4 turn back. I watch the carb to see if it's syphoning. I plug the fill line right away. When I'm starting a brand new model or brand new engine for the first time, I make careful note of whether or not it is dry when the starter is applied. If it is, I play around next time I crank it to see if priming is needed or not and what method works.

It sounds like a lot of things, but they're things that take no time at all and make for better times later on.

If you really can't get the hang of a balky starting engine, I got another piece of advice. Stand up, look around at your flying buddies and yell, "HEY ANY OF YOU GUYS EVER FLY CL STUNT????" <GRIN> And another "pearl of wisedom"..... don't ask help from anyone who has inverted engines and bandaids on his fingers.